Current Status and Prospects of Vertical Deflection Measurement Methods

Vertical deflection is a core parameter for describing the Earth's shape and gravity field characteristics, holding significant importance in geodesy, geophysics, geological hazard monitoring, and marine sciences. This paper systematically reviews the main methods for measuring vertical deflection, including astronomical geodetic methods, GNSS leveling, gravimetric methods, spherical harmonic solutions of the gravity field, and satellite altimetry inversion. The advantages, disadvantages, and applicability of each method are analyzed. Among these, direct measurement methods (such as astronomical geodesy, integrated GNSS with CCD technology, and GNSS/leveling measurements) can achieve high-precision vertical deflection measurements due to their real-time data acquisition capabilities, but they are limited by environmental conditions and equipment performance. On the other hand, indirect measurement methods (such as gravimetric methods, spherical harmonic solutions of the gravity field, and satellite altimetry) use existing data for calculations, offering higher computational efficiency, but their accuracy depends on high-precision, high-resolution gravity field models or the quality of input data. In general, astronomical geodetic methods (integrated GNSS with total stations for DOV measurements, and integrated GNSS with CCD for DOV measurements) remain the primary approach for directly measuring high-precision vertical deflections and are suitable for high-precision requirements in static environments. GNSS leveling methods have been widely applied in ground measurements and regional mapping, but their application is challenging in complex terrain conditions. Spherical harmonic solutions of the gravity field and satellite altimetry methods, with their broad coverage advantages, play a key role in marine vertical deflection measurement and global gravity field research. However, each method has certain limitations, and the need for all-weather, high-precision, automated vertical deflection measurements remains a pressing challenge. Due to the limitations of existing methods in complex weather conditions, particularly the demand for high-precision measurements in all-weather conditions, this paper focuses on the development potential of all-weather vertical deflection measurement methods. It elaborates on a new all-weather vertical deflection measurement method that integrates GNSS with three-dimensional laser tracking technology. Finally, by considering the advances in instrumentation and data processing technologies, the paper looks forward to the future development trends in vertical deflection measurement. It highlights that the miniaturization and commercialization of astronomical geodetic equipment, the application of all-weather vertical deflection measurement methods, and breakthroughs in marine vertical deflection measurement techniques will be key research directions in the future. Through equipment innovation, technological integration, and expansion into multiple fields, vertical deflection measurement technology will play an even greater role in supporting Earth science research and meeting practical engineering needs.